1. To view the key you need to redeem, right click on Soldier Front 2 in your Steam library, and then click on "view CD key".
2. Go to http://Soldierfront2.aeriagames.com/itemmall/free-rewards/gift/3. Log in with your Aeria Games account
4. Type in your redemption key (CD key from Steam)
5. Click on Redeem
6. It’s done! Your item will be sent directly in game